Phosphor screen assembly

ABSTRACT

An image intensifier tube including a source of electrons, an electron amplifier and a phosphor screen assembly, the tube including connecting a source of electrical potential across the electron amplifier and the screen assembly to create an electric field therebetween to accelerate the electron flow between the electron amplifier and the screen assembly. The phosphor screen assembly includes a metal film forming a plate and a phosphor film for translating the electron flow to a viewable image. Both films are attached to a glass substrate forming the viewing surface. An additional metallic film is attached to the opposite side of the glass to that supporting the phosphor screen for balancing the effect of the electric field on the phosphor screen assembly, thus minimizing flaking of certain portions of the phosphor screen assembly.

United States Patent [191 Goodrich PHOSPHOR SCREEN ASSEMBLY [75] Inventor: George W. Goodrich, Bloomfield Hills, Mich.

[73 Assignee: The Bendix Corporation, Teterboro,

[22] Filed: July 12, 1968 [2]] Appl. No.: 744,360

[ Nov. 13, 1973 Primary Examiner-Benjamin R. Padgett Assistant Examiner-J. Potenza Attorney-Flame, l-lartz, Smith & Thompson [57] ABSTRACT An image intensifier tube including a source of electrons, an electron amplifier and a phosphor screen assembly, the tube including connecting a source of electrical potential across the electron amplifier and the screen assembly to create an electric field therebetween to accelerate the electron flow between the electron amplifier and the screen assembly. The phosphor screen assembly includes a metal film forming a plate and a phosphor film for translating the electron flow to a viewable image. Both films are attached to a glass substrate forming the viewing surface. An additional metallic film is attached to the opposite side of the glass to that supporting the phosphor screen for balancing the effect of the electric field on the phosphor screen assembly, thus minimizing flaking of certain portions of the phosphor screen assembly.

7 Claims, 2 Drawing; Figures rrrosrrron SCREEN ASSEMBLY BACKGROUND AND SUMMARY OF THE INVENTION This invention relates generally to an electron accelerator assembly and more particularly to a field balancing apparatus which is particularly adapted for utilization in an image intensifier tube.

In the past, image intensifier tubes have been utilized to increase the amount of electron energy imparted to the phosphor screen by increasing the number and speed of the electrons, thus increasing the intensity of the image formed on the phosphor screen. The image intensifier tubes have generally been formed with a source of electrons which is adapted to scan an entrance end of a micro-channel array, the microchannel array being utilized to amplify the electron flow from the source of electrons. Further, as the electrons leave the exit end of the microchannel array, an electric field is created between the array and the phosphor screen to accelerate the electrons in the space between the array and the phosphor screen. The subsequent high energy impingement of the electrons on the phosphor screen assembly causes an image to be formed which may be viewed through a glass support or substrate member.

The phosphor screen assembly generally includes a thin phosphor layer attached to the glass substrate and a metal film evaporated on the phosphor layer to form th second plate for the accelerating field between the array and the phosphor screen assembly. However, it has been found that the metal film, and in certain cases the phosphor film, has a tendency to flake off or cause Stratification of the phosphor layer due to the high field developed between the micro-channel array and the metal film. The above noted flaking or stratification is caused by the attraction between the metal film and the micro-channel array, the attractive force being created by the high intensity field.

It has been found that the phosphor layer may be strengthened by including a binder, for example potassium silicate, thus minimizing the Stratification of the phosphor layer. However, the flaking of the thin metallic film still occurs due to the relatively light attaching force between the metallic film and the phosphor layer, this attaching force being similar to the force created by a static electric charge.

In accordance with certain features of the present invention, it has been found that the above noted flaking and stratification may be minimized and substantially eliminated by providing a balancing field to that created between the micro-channel array and the metallic film. In practice, this balancing field has been created by providing the glass substrate with a relatively transparent metal or nesa film on the opposite side of the glass substrate to that occupied by the phosphor film.

This latter metallic film is placed at an electrical voltage which is of the same polarity as the micro-channel array relative to the metal film attached to the phosphor screen, and is of sufficient magnitude to create a field between the metallic film on one side of the glass substrate and the transparent film on the opposite side of the glass substrate which is substantially equal to the accelerating field. Obviously, the force on the metallic film on the phosphor film side of the glass substrate may be increased or decreased by increasing or decreasing, respectively, the intensity of the field across the glass substrate relative to the field created between the micro-channel array and the evaporated film.

Accordingly, it is one object of the present invention to provide an improved electron accelerating assembly.

It is another object of the present invention to provide an improved electron accelerating assembly having relatively balanced fields.

It is still a further object of the present invention to provide an improved phosphor screen assembly for image intensifying tubes.

It is still another object of the present invention to provide an auxiliary field for an image intensifier tube which minimizes or eliminates the flaking effect within the phosphor screen assembly.

Further objects, features and advantages of this invention will become apparent from a consideration of the following description, the appended claims and the accompanying drawing in which:

FIG. 1 is a schematic diagram II'll representative form illustrating a portion of certain heretofore utilized image intensifier tubes; and

FIG. 2 illustrates the portion of an image intensifier tube of FIG. 1 further incorporating the features of the present invention.

Referring now to the drawing, there is illustrated a portion of an image intensifier tube 8 which includes a micro-channel array I0 for amplifying a stream of electrons from an electron source (not shown), and a phosphor screen assembly 12 for transforming the electron stream into a visual image. It is to be understood that the assemblies of FIGS. 1 and 2 are merely representative as to size and spacing. The micro-channel array 10 may be formed of any plurality of single electron multiplier tubes formed in an array assembly.

The phosphor screen assembly 12 is illustrated as being spaced from the micro-channel array It), the phosphor screen assembly including a glass substrate member 14, a phosphor layer 16 and an evaporated metallic film layer 18. The layers 16 and 18 are attached to the electron impingement side of the glass substrate member 14, the phosphor layer being approximately 10 microns thickand is attached to the glass substrate 14 in any suitable manner. As stated above, the phosphor layer may be further strengthened by including a binder with the phosphor material.

The layer 18 is normally formed from aluminum which is evaporated onto the phosphor layer in a thin layer, in the order of 1,000 angstrom units, so that the film is transparent to the electron flow. The film is attached to the phosphor layer 16 by a very light force and is utilized to form a metallic plate for creating an accelerating field between the micro-channel array I0 and the phosphor layer 16. The field is established between the micro-channel array and the phosphor screen assembly by grounding the array 10 at ground conncection 20 and by applying a I0 kilovolt potential to the aluminum layer 18.

Referring now to FIG. 2, there is illustrated an intensifier tube assembly including the micro-channel array 10 discussed in conjunction with FIG. I and a modified phosphor screen assembly 26 incorporating the fea tures of the present invention. In particular, the microchannel array 10 is spaced from the aluminum film 1% and phosphor film 16, both of which are attached to the back side of the glass substrate M, as described in conjunction with FIG. ll. However, an additional film 2b is added to the front side of the glass substrate M, for a purpose to be hereinafter explained, the film being formed of tin oxide or evaporated manganese to form an optically invisible film on the outside face of the glass substrate 14.

Accordingly, the micro-channel array amplifies elec tron flow from the source of electrons (not shown), and the electrons emitting from the micro-channel array are accelerated to the phosphor screen 16 by means of a field developed between the micro-channel array 10 and the aluminum film 18. As was the case with FIG. 1, the micro-channel array is grounded at and the aluminum film 18 is provided with a positive 10 kilovolt potential to create the accelerating field. The accelerated electrons are driven through the aluminum film 18, the aluminum film being transparent to the flow of electrons, to cause a phorphorescent effect at the phosphor film 16. In this way an image is formed in accordance with the magnitude and speed of the electron flow fom the micro-channel array 10.

As stated above, the field between the mcro-channel array and the film 18 causes a flaking of the film 18 due to the electrostatic forces created by the accelerating field. In order to overcome this flaking or the Stratification of the phosphor film 16, the film 28 is connected to a potential which is of such a magnitude and polarity to create a field, and thus a force on film 18, to balance or exceed the force on film 18 due to the field created by the potential between array 10 and film 18. Thus, the film 18 has a zero force tending to pull the film 18 away from the phosphor layer 16 or may have a force acting thereon tending to increase the attachment of the film to the layer 16. In the latter case, this force will also increase the attachment of the layer 16 to the glass substrate 14.

Obviously, the force between the layers 18 and 28 is a function of many factors such as the dielectric constant of glass as compared to the dielectric of the space between array 10 and film 18, the spacing between film l8 and film 28 and the relative areas of the films, although it is contemplated that the areas would be substantially equal. Also, the relative potential applied to film 28 will greatly vary the force on film 18. For illustrative purposes, the film 28 is shown as being grounded through connection 30. However, it is contemplated that, consistent with safety, the film 28 may be connected to any magnitude or polarity potential to achieve the desired result.

While it will be apparent that the embodiment of the invention herein disclosed is well calculated to fulfill the objects of the invention, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope or fair meaning of the subjoined claims.

What is claimed is:

1. An image transducer comprising:

a screen assembly;

first means for establishing a substantial electric field proximate said screen assembly which tends to produce a deleterious efi'ect on said screen assembly; and

second means for establishing a second electric field counteracting the effect of said first electric field on said screen assembly.

2. The invention of claim 1 wherein said screen assembly is a multilayer screen assembly, and said deleterious effect is a flaking of at least one layer of said multi-layer screen assembly due to electrostatic forces created by said first field and said second field counteracts said electrostatic forces.

3. The invention of claim 2 wherein:

said multi-layer screen assembly includes a support layer and a phosphor layer positioned on one side of said support layer; and

said second field establishing means includes a first conductive film positioned on the opposite side of said support layer to the side supporting said phosphor layer.

4. The inventon of claim 4 wherein said second field is at least as great as said first field.

5. The invention of claim 3 wherein:

the image transducer includes an electrode spaced from said screen assembly; and

said fist electric field is utilized to accelerate electrons between said electrode and said screen assembly.

6. The invention of claim 5 wherein said first conductive film is optically transparent.

7. The invention of claim 6 wherein:

said screen assembly includes a second conductive film transparent to the passage of electrons positioned on the side of said phosphor layer closest to said electrode; and said flaking comprises the flaking of said second conductive film. 

1. An image transducer comprising: a screen assembly; first means for establishing a substantial electric field proximate said screen assembly which tends to produce a deleterious effect on said screen assembly; and second means for establishing a second electric field counteracting the effect of said first electric field on said screen assembly.
 2. The invention of claim 1 wherein said screen assembly is a multilayer screen assembly, and said deleterious effect is a flaking of at least one layer of said multi-layer screen assembly due to electrostatic forces created by said first field and said second field counteracts said electrostatic forces.
 3. The invention of claim 2 wherein: said multi-layer screen assembly includes a support layer and a phosphor layer positioned on one side of said support layer; and said second field establishing means includEs a first conductive film positioned on the opposite side of said support layer to the side supporting said phosphor layer.
 4. The inventon of claim 4 wherein said second field is at least as great as said first field.
 5. The invention of claim 3 wherein: the image transducer includes an electrode spaced from said screen assembly; and said fist electric field is utilized to accelerate electrons between said electrode and said screen assembly.
 6. The invention of claim 5 wherein said first conductive film is optically transparent.
 7. The invention of claim 6 wherein: said screen assembly includes a second conductive film transparent to the passage of electrons positioned on the side of said phosphor layer closest to said electrode; and said flaking comprises the flaking of said second conductive film. 